The Development of the Joint NASA GSFC and the National Imagery and Mapping Agency (NIMA) Geopotential Model EGM96

TLDR

EGM96 was produced by a joint effort of NASA GSFC, NIMA, and OSU, combining surface gravity, altimeter‑derived anomalies from ERS‑1, GEOSAT, and TOPEX/POSEIDON, satellite tracking from SLR, GPS, TDRSS, DORIS, and TRANET, and blending a low‑degree model to degree 70 with block‑diagonal and quadrature solutions up to degree 360. EGM96 delivers geoid undulations accurate to better than one meter (except in data‑poor regions), realizes WGS84 as a true 3‑D reference system, provides degree‑20 dynamic ocean topography from T/P and ERS‑1, and improves orbit determination for Earth‑orbiting satellites.

Abstract

The NASA Goddard Space Flight Center (GSFC), the National Imagery and Mapping Agency (NIMA), and The Ohio State University (OSU) have collaborated to develop an improved spherical harmonic model of the Earth's gravitational potential to degree 360. The new model, Earth Gravitational Model 1996 (EGM96), incorporates improved surface gravity data, altimeter-derived gravity anomalies from ERS-1 and from the GEOSAT Geodetic Mission (GM), extensive satellite tracking data-including new data from Satellite Laser Ranging (SLR), the Global Postioning System (GPS), NASA's Tracking and Data Relay Satellite System (TDRSS), the French DORIS system, and the US Navy TRANET Doppler tracking system-as well as direct altimeter ranges from TOPEX/POSEIDON (T/P), ERS-1, and GEOSAT. The final solution blends a low-degree combination model to degree 70, a block-diagonal solution from degree 71 to 359, and a quadrature solution at degree 360. The model was used to compute geoid undulations accurate to better than one meter (with the exception of areas void of dense and accurate surface gravity data) and realize WGS84 as a true three-dimensional reference system. Additional results from the EGM96 solution include models of the dynamic ocean topography to degree 20 from T/P and ERS-1 together, and GEOSAT separately, and improved orbit determination for Earth-orbiting satellites.